1. Field of the Invention.
This invention relates in general to storage systems, and more particularly to a method and apparatus for compensating for multiple thermal asperity events in a sector.
2. Description of Related Art.
Computers often include auxiliary memory storage units having media for data storage and retrieval. Disk drives are the most common example of such auxiliary memory storage units. Disk drives typically include stacked, commonly rotated rigid magnetic disk for magnetically recording data thereon. Data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the drive axis write data to and read data from the disks. A slider supports one or more magnetic heads. The slider is lightly biased to cause the heads to move toward the recording surface when the disk is stationary; but as the disk is brought up to operating speed, an air bearing is generated which moves each slider and hence the heads away from the recording surface toward a preselected flying height. Achievement of a higher data density on magnetic disks has imposed increasingly narrow transducing gaps.
Magneto-resistive (MR) heads have substantially improved the areal bit densities of hard disk drives. However, this improvement is not without complications. More specifically, MR heads have been associated with an increased sensitivity to thermal asperities. Contact with debris or media bumps can heat up MR heads, causing disturbances in the read-back signal. Near contacts with mounts on the media can cool down MR heads, causing disturbances in the read-back signal. Unless properly compensated for, these disturbances can produce unrecoverable errors.
A heating thermal asperity occurs when a head contacts a disk asperity or collides with a foreign particle. A cooling thermal asperity occurs when a head has a near contact with a disk asperity which causes a heat transfer out of the MR element. While thermal asperities can occur with inductive heads, they are a more serious problem in MR heads. For example, thin-film heads generate current based on changes in the magnetic flux. The inductance value is not significantly affected by temperature, and the change in series resistance is a second-order effect.
In contrast, the fundamental read-back mechanism of an MR head is inherently sensitive to changes in temperature. MR heads are resistive sensors, which generate resistive variations, and corresponding voltage or current variations, in response to changes in the magnetic field of the media. MR head stripes are made of permalloy. Like most metals, the resistivity of permalloy is proportional to temperature. Unfortunately, this change in resistance resulting from a thermal asperity has similar characteristics to the read-back signal the sensor is designed to detect.
Asperity problems are further compounded by efforts to push areal densities higher and to maintain adequate signal-to-noise ratios. Such trends have led to lower flying heights, creating additional problems for disk-drive manufacturers. This is true even though significant improvements have been made in media smoothness and contamination control.
Many approaches have been developed for detecting and compensating for thermal asperity transients. In fact, these thermal asperity techniques have made single thermal asperity occurrence per sector in a hard disk drive with MR heads a non-event. However, up to now, thermal asperity handling techniques have not been able to fully compensate for multiple thermal asperity events occurring in a single sector, and hard error events are still a common incident.
It can be seen that there is a need for a method and apparatus that compensates for multiple thermal asperity events occurring in a sector.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for compensating for multiple thermal asperity events in a sector.
The present invention solves the above-described problems by providing for the detection, logging and recovery from errors caused by multiple thermal asperities occurring in a single sector.
A method in accordance with the principles of the present invention includes detecting thermal asperity events in a sector, setting a flag indicating occurrence of a thermal asperity event in the sector, maintaining a count of the detected thermal asperity events in the sector and recording a location for the detected thermal asperity event in the sector.
Other embodiments of a system in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the method further includes performing a data recovery procedure in response to the detected thermal asperity event.
Another aspect of the present invention is that the data recovery procedure is performed using the flag settings and a location corresponding to the detected thermal asperity events.
Another aspect of the present invention is that the data recovery procedure is further performed using the count of the detected thermal asperity events.
Another aspect of the present invention is that the setting of a flag includes setting a bit in a register.
Another aspect of the present invention is that the recording further comprises setting a selected bit in a register, the selected bit""s position in the register being determined by the location of the detected thermal asperity event.
Another aspect of the present invention is that the maintaining a count of the detected thermal asperity events in the sector includes the setting of a bit in the register for each detected thermal asperity event, the count being equal to a number of bits set in the register.
Another aspect of the present invention is that the recording of the location for the detected thermal asperity event in the sector includes setting a bit in a register, the bit being associated with the asperity event.
Another aspect of the present invention is that the maintaining a count of the detected thermal asperity events in the sector includes setting a bit in a register for each detected thermal asperity events, the count being equal to a number of bits set in the register.
In another embodiment, the present invention includes a controller for processing multiple asperity events in a sector of a storage device, the controller including a processor for receiving indications of thermal asperity events in a sector and a register for storing an indication representing each occurrence of a thermal asperity event in the sector.
In another embodiment, the present invention includes a disk drive, the disk drive including a storage medium including sectors of recorded data, a motor for moving the storage medium relative to a magneto-resistive head and a control unit, the control unit controlling the motor and the position of the magnetic head relative to the data storage medium and a controller for processing multiple asperity events in a sector of the storage medium, the controller further including a processor for receiving indications of thermal asperity events in a sector and a register for storing an indication representing each occurrence of a thermal asperity event in the sector.